Obsessive-compulsive disorder (OCD) is a debilitating mental illness that seriously undermines an individual's daily functioning, and causes enormous social and economic losses estimated to be $8.4 billion annually in the US alone. Although effective behavioral and pharmacological treatments exist for OCD, a significant portion of patients with OCD (40-60%) refuse to receive, drop out of, or otherwise fail to respond to the currently most efficacious treatments. Suboptimal clinical outcomes and under-utilization of these treatments result from practical barriers such as adverse effects (e.g., intense distress during the exposure procedure or side effects of medication), high costs for treatment, and a lack of therapists trained in existing treatments. Thus, there is an urgent need for developing effective, non-aversive, cost-efficient, and portable treatment approaches for OCD. The objective of this R21 application is to examine the feasibility of a computerized cognitive trainin program focused on improving response inhibition (RI) in order to improve OCD symptoms. There is compelling evidence that poor RI is a core cognitive feature of OCD, but no effective intervention exists that directly attempts to address this problematic cognitive deficiency. This application proposes to conduct a preliminary randomized trial with two arms, in which 30 unmedicated OCD patients without major psychiatric comorbidity will be randomly assigned to 8 45-min sessions of (a) computerized response inhibition training (RIT) or (b) placebo computer training (PLT). To this end, two specific aims and an exploratory aim are proposed. Specific Aim 1 is to determine the effectiveness of computerized RIT in enhancing RI among OCD patients. Specific Aim 2 is to determine the effectiveness of computerized RIT in improving OCD symptoms. The exploratory aim is to evaluate subjective treatment experiences and patient retention of the proposed RIT. Completion of this proposed project will yield preliminary data evaluating the utility of computerized RIT as a potentially effective clinical intervention for OCD This contribution is significant because detecting the therapeutic signal of cognitive training for OCD will lay the groundwork for developing effective, cost-efficient, and disseminable adjunctive interventions for OCD to enhance existing treatments, and a potentially effective stand-alone computerized intervention for OCD characterized by good treatment acceptability, portability, and patient retention. The research proposed in this application is innovative because it proposes a fundamentally different therapeutic approach to OCD using a novel computer-based cognitive training program to enhance poor RI and reduce OCD symptoms. In sum, this project is expected to generate important knowledge to guide the development of effective computer-based treatment approaches that may help reduce critical problems of existing treatments such as suboptimal patient retention and treatment under-utilization, thereby improving overall treatment response rates among individuals suffering from OCD.